The present disclosure relates to a detecting device, a power supply system, and a detecting device control method, and specifically relates to a detecting device, a power supply system, and a detecting device control method, which detect a foreign object within a magnetic field.
Recently, a power supply system, which supplies power to a consumer electronics (CE) device such as a cellular phone, portable music player, or the like in an electrically noncontact manner, has received attention. This power supply system has been referred to as a noncontact power supply system, noncontact power transmission system, or wireless power supply system. This system enables a secondary-side device such as an electronic device or the like to be charged using a simple method such that placing the secondary-side device on a primary-side device such as a power supply device or the like. That is to say, this system eliminates terminal connection between the electronic device and power supply device.
Electromagnetic induction has been widely used as a method to perform supply of power in such a noncontact manner. Lately, a noncontact power supply system, which employs magnetic field resonance (or magnetic resonance) utilizing the resonance phenomenon, has also received attention.
The noncontact power supply system using the magnetic field resonance method has an advantage over the electromagnetic induction method in that transmission of power can be performed between devices with more distance therebetween, utilizing a principle called the resonance phenomenon. Also, the noncontact power supply system using the magnetic field resonance method has an advantage such that power transmission efficiency (that is, power supply efficiency) does not deteriorate even when axial matching is poor between a power supply coil serving as the power supply source and a power reception coil serving as the power supply destination.
However, the fact remains that both the magnetic field resonance method and electromagnetic induction method are noncontact power supply systems utilizing magnetic coupling between a power supply coil serving as the power supply source and a power reception coil serving as the power supply destination.
Incidentally, there have been developed heat generation countermeasures regarding foreign objects such as metal, magnetic materials, magnets, and so forth, which may generate heat due to magnetic field lines, as one of important factors in the noncontact power supply system. Upon a foreign object entering the gap between the power supply coil and power reception coil in the noncontact power supply system in the electromagnetic induction method or magnetic field resonance method, there is a possibility that the foreign object will generate heat due to magnetic field lines passing through this foreign object. Such heat generation of the foreign object is caused due to overcurrent loss generated at a metal foreign object through which the magnetic field lines pass, hysteresis loss generated at a foreign object magnetic material or foreign object magnet or the like through which magnetic field lines pass, or the like.
Since the heat generation of a foreign object may lead to malfunction or damage or the like of the power supply device or electronic device, prevention of heat generation of the foreign object can be said to be a major issue in the noncontact power supply system.
Though there is a technique to deal with this heat generation, which involves adding a temperature sensor to detect the heat generation of a foreign object, this technique is far from being a fundamental solution for the heat generation of a foreign object, since this technique detects the temperature of a foreign object which has already been heated. That is to say, a method for enabling detection of a foreign object before the foreign object excessively generates heat, is desirable as a method for detecting a foreign object which may generate heat due to magnetic field lines.
Therefore, there has been proposed a technique for determining whether or not there is a metal foreign object, by monitoring electrical parameters (current, voltage, and so forth) which will change when a metal foreign object enters between the power supply side and power reception side. Such a technique enables detection of whether or not there is a foreign object, before the foreign object excessively generates heat. Specifically, there has been proposed a technique for detecting a metal foreign object, by monitoring change in amplitude and phase at the time of communication between the power supply side and power reception side (e.g., see Japanese Unexamined Patent Application Publication No. 2008-206231). Also, a method for detecting a metal foreign object according to overcurrent loss has been proposed (e.g., see Japanese Unexamined Patent Application Publication No. 2001-275280).